The present invention concerns an automatic selector device, and more particularly, an automatic selector device for a change-speed gearbox of the epicyclic type, having frictional selector apparatus configured to be engaged by a selector actuator of axial piston type between plural gearbox elements rotatable relative to one another, comprising a selector valve for application of working pressure to the selector actuator and an electromagnet switch-over control valve configured to be electronically triggered to switch over the selector valve, both the selector valve and the switch-over control valve are arranged to be respectively switched over between a rest position selectable by spring force and a working position. The selector actuator is connected to a pressure-relieved zero connection in the rest position of the selector valve and is connected to a system pressure conduit carrying a controlled system pressure in the working position, while a control connection of the selector valve used for switching over into the rest position is connected to a pressure-relieved zero connection in the rest position of the switch-over control valve and connected to a control pressure supply conduit carrying a control pressure in the working position of the switch-over control valve.
A selector device is described in ATZ Automobiltechnische Zeitschrift 88 (1986) 12, p. 681. The known selector device consists of an electronic part and a hydraulic part. Whereas the hydraulics are responsible, among other things, for applying pressure to the currently actuated selector actuators, the electronics control the gear change and also, to some extent, regulate the level of the hydraulic pressure. The connection between the electronics and the hydraulics is usually achieved by electromagnetic 3/2-way switch-over control valves. These are designed in such a way that when they are excited, i.e. when an electric current flows through their coil, the associated selector actuator is subjected to hydraulic pressure.
In the known selector device, interruption of the electric current to the switch-over control valves, whether due to a defect in the electronic control or due to the failure of the voltage supply, leads to interruption of the force path. This can produce dangerous driving situations because either, in overrun, the engine brake (and possibly a retarder located in front of the gearbox) becomes ineffective or, when the engine is in traction, the engine torque is no longer available on a gradient.
In order to avoid the problem described, it has been considered to use so-called locking solenoid valves equipped with a permanent magnet which ensures that, in the absence of an electrical supply, the solenoid valve remains in one position once it has been reached. Switching over into the respective other position takes place by way of a short selection pulse whose sign defines the switching position.
In addition to the more complicated design of the electromagnetic valve and the necessary triggering by a reversible current direction, the foregoing proposal has the disadvantage that the switching position of the valve is not unambiguous when there is no current flowing through the coil. It could happen, for example, that a valve previously in the activated position could move unintentionally into the deactivated position due to vibrations, external magnetic fields and the like, so that the relevant selector actuator again becomes unpressurized.
Even more serious is the problem of defined deactivation. Should the electrical connection to a solenoid valve have been interrupted, the solenoid valve and, therefore, the associated selector actuator can no longer be deactivated so that, for example, it is more difficult to tow the vehicle, or the gearbox could even be jammed if a different selector actuator were activated.
An object on which the present invention is based consists essentially in ensuring that the selector actuator which has just been actuated remains subjected to working pressure even in the case of a failure of the electrical voltage supply. When the engine is switched off, the selector device takes up such a position that when the engine is restarted, the selector actuators remain unpressurized.
The foregoing object has been achieved in an advantageous manner according to the present invention by providing that the selector valve is configured to be additionally moved into the rest position by the control pressure of the switch-over control valve and additionally into the working position by a control pressure dependent on the working pressure of the selector actuator and includes the respective control connections, the switch-over control valve is configured to be brought only into the working position in phases and is in the rest position in the steady-state condition, consisting of one of the completely engaged condition and completely disengaged condition of the selector apparatus, and a change control valve has a valve connection for a control pressure conduit leading to the control connection of the selector valve for movement thereof into the working position, a valve connection for a control pressure conduit leading to the control connection of the selector valve for movement thereof into the rest position, a valve connection for a control pressure conduit leading to the switch-over control valve and a valve connection for pressure relief and can be switched over between a rest position in which the valve connection for the control pressure conduit is connected to the valve connection for pressure relief to move the selector valve into its rest position and the valve connection for the control pressure conduit is connected to the valve connection for the control pressure conduit leading to the switch-over control valve to move the selector valve into its working position, and a working position in which the valve connection for the control pressure conduit is connected to the valve connection for the control pressure conduit leading to the switch-over control valve to move the selector valve into the rest position and the valve connection for the control pressure conduit is connected to the valve connection for pressure relief to move the selector valve into the working position, and the change control valve is switched over, as a function of the condition of the selector apparatus, such that the valve connection of the change control valve for the control pressure conduit leading to the switch-over control valve is necessarily connected in the one steady-state condition of the selector apparatus to the respective valve connection for the control pressure conduit to switch over the selector valve into one of the rest and working positions bringing the selector apparatus into the other steady-state condition.
In the selector device according to the present invention, the switch-over control valve is always in its rest position in the steady-state condition of the selector device so that an electronic or voltage failure does not change anything relative to the selector condition. The selector valve is held in its rest position by spring force in the disengaged condition of the selector device and is held in its working position in the engaged condition by the self-retention effect of the relevant control pressure dependent on the working pressure. The change control valve is always moved in advance, as a function in each instance of the instantaneous steady-state condition of the selector device, into the position in which, on excitation of the switch-over control valve, the selector valve is switched over into the position for the respective other selector condition, i.e. not the instantaneous steady-state selector condition. When the engine is switched off, the pressure supply is also switched off so that the selector valve and the change control valve are also moved by spring force into the respective rest position. As a result, the selector actuators remain unpressurized when the engine is restarted.
The control, according to the present invention, of the change control valve as a function of the steady-state condition of the selector device can be implemented in several ways. One advantageous embodiment for achieving this control provides that the change control valve can be the change control valve is configured to be moved into each of the rest and working positions by a position control pressure and has respective control connections, and a position control valve has a valve connection for a control pressure conduit leading to the control connection of the change control valve to move it into the rest position, a valve connection for a control pressure conduit leading to the control connection of the change control valve to move it into the working position, a valve connection for a control pressure supply conduit is arranged to carry a control pressure and a valve connection for pressure relief and is configured to be switched over between a rest position, in which the valve connection for the control pressure conduit is connected to the valve connection for the control pressure supply conduit to move the change control valve into its rest position and the valve connection for the control pressure conduit is connected to the valve connection for pressure relief to move the change control valve into its working position, and a working position, in which the valve connection for the control pressure conduit is connected to the valve connection for pressure relief to move the change control valve into its rest position and the valve connection for the control pressure conduit is connected to the valve connection for the control pressure supply conduit to move the change control valve into its working position, and the position control valve is configured to be moved by spring force into its rest position and moved into its working position by a control pressure dependent on the working pressure of the selector actuator.
The arrangement of the present invention can be applied to avoid premature switching over during the transient condition, i.e. during the engagement or disengagement of the selector apparatus, when the above-mentioned embodiment of the control of the change control valve is used. It is assumed that the switch-over control valve is in its rest position only in the steady-state condition of the selector.
In order to simplify the structural control complexity a multiway double valve, e.g. a 7/2-way double valve, in which the selector valve and position control valves are structurally combined can be effectively utilized.
An arrangement for disengaging a first frictional selector having a first selector device and for simultaneously engaging a second frictional selector having a second selector can be used to ensure, in gear changes with positive overlap of the variation in the working pressures for the disengagement of one selector by the first selector device according to the invention and the simultaneous engagement of a selector by the second selector device according to the invention, that in the case of an electrical defect, the activating or deactivating selector actuator whose working pressure is sufficient to transmit the necessary torque is the one which always remains actuated. This overlap control also prevents the two selectors involved from ever being engaged simultaneously which would otherwise cause the gearbox to jam.
In the case of a failure of the electrical system during the filling procedure at the selector actuator of the selector to be engaged, the filling procedure is interrupted and the selector actuator is emptied, whereas the selector actuator of the selector engaged, whose associated switch-over control valve is not excited in any event, remains activated.
The self-retention effect at the selector valve of the selector to be engaged is sufficiently high for the latter, or the new gear, to remain engaged only in the case where the working pressure of the selector actuator of the selector to be engaged is so high that the selector valve of the selector to be disengaged is moved into the rest position.
In the case of overlap control, the structural control complexity in the selector device according to the invention can again be kept low by a further multiway double valve.